In the conventional construction of a master frame for windows the header and the sill are joined to side frames by the use of welding. Generally, the various pieces forming the frame are mitre cut at a 45.degree. angle and the welding operation which secures the pieces together has the disadvantages of leaving flash material. In addition, this conventional welding method for mounting the pieces together is also relatively time consuming and costly. It would be desirable to provide a method of forming a master frame wherein the various conventional pieces could be secured together in a quick and economical manner and in a manner which leaves a clean final product without the undesired flashing.